Method for adsorbing fluorocarboxylic acid having ether bond and method for collecting same

Abstract

Disclosed are an adsorption process whereby a fluorocarboxylic acid having an ether bond can be adsorbed to a high extent by using active carbon without changing the form thereof, and a desorption process whereby the adsorbed material can be desorbed from the active carbon to thereby enable the reuse of the active carbon and the adsorbed material. In the aforesaid processes, a solution containing a fluorocarboxylic acid having an ether bond is contacted with active carbon and thus the active carbon is allowed to adsorb the fluorocarboxylic acid, to thereby give a solution having a small fluorocarboxylic acid content. Then, the active carbon having adsorbed the fluorocarboxylic acid is heated to thereby desorbs the fluorocarboxylic acid from the active carbon.

The invention claimed is:  
     
       1. A method of adsorbing a fluorocarboxylic acid having an ether bond, which comprises contacting an aqueous containing fluorocarboxylic acid solution with an acidic high activation active carbon to adsorb the fluorocarboxylic acid by the acidic high activation active carbon,
 wherein the acidic high activation active carbon is produced by soaking, in an acid, an active carbon, or by flowing the acid through the active carbon, in which the active carbon has been subjected to an activation treatment, and 
 wherein the acidic high activation active carbon has an adsorption rate of the fluorocarboxylic acid of 10% or more; and 
 wherein the fluorocarboxylic acid having an ether bond is represented by the following general formula (I):
   X—Rf—COOH   (I)
 
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, and 
 Rf is a group having a linear or branched monooxyfluoroalkylene group or polyoxyfluoroalkylene group having 4-20 carbon atoms. 
 
     
     
       2. The method according to  claim 1 , wherein the acidic high activation active carbon has a specific surface area of at least 1500 m 2 /g. 
     
     
       3. The method according to  claim 1 , wherein the pH of the acid solution contacting with the active carbon during the preparation of the active carbon is adjusted to at most 4. 
     
     
       4. The method according to  claim 1 , wherein Rf is a group of the formula:
   -A 1 O-(A 2 O) n -A 3 - 
 wherein A 1 O is an oxyfluoroalkylene group having 1-10 carbon atoms, 
 A 2 O is an oxyfluoroalkylene group having 2-5 carbon atoms, 
 A 3  is a fluoroalkylene group having 1-4 carbon atoms, and 
 n is an integer of 0 to 5, preferably an integer of 1 to 4. 
 
     
     
       5. The method according to  claim 1 , wherein the fluorocarboxylic acid is represented by the following general formula (II):
   X—(CF 2 ) m —O—(CF(CF 3 )CF 2 O) n —CF(—Y)(CF 2 ) p COOH   (II)
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, 
 Y is a hydrogen atom, a fluorine atom or CF 3 , 
 m is an integer of 1 to 10, 
 n is an integer of 0 to 5, and 
 p is 0 or 1. 
 
     
     
       6. The method according to  claim 1 , wherein the fluorocarboxylic acid is represented by the following formula (IIa) or (IIb):
   X—(CF 2 ) m —O—(CF(CF 3 )CF 2 O) n —CF(CF 3 )COOH   (IIa)
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, 
 m is an integer of 1 to 10, and 
 n is an integer of 0 to 5, or
   X—(CF 2 ) m —O—(CF(CF 3 )CF 2 O) n —CHFCF 2 COOH   (IIb)
 
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, 
 m is an integer of 1 to 10, and 
 n is an integer of 0 to 5. 
 
     
     
       7. The method according to  claim 1 , wherein the fluorocarboxylic acid having an ether is CF 3 —O—CF(CF 3 )CF 2 O—CF(CF 3 )COOH. 
     
     
       8. The method according to  claim 1 , wherein the fluorocarboxylic acid is 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxyl]-propanoic acid or salts thereof. 
     
     
       9. A method of recovering a fluorocarboxylic acid having an ether bond, which comprises desorbing the fluorocarboxylic acid having an ether bond from an acidic high activation active carbon, which has adsorbed the fluorocarboxylic acid b the use of azeotropy, with water to collect the fluorocarboxylic acid,
 wherein the acidic high activation active carbon has an adsorption rate of the fluorocarboxylic acid of 10% or more; and 
 wherein the fluorocarboxylic acid having an ether bond is represented by the following general formula (I):
   X—Rf—COOH   (I)
 
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, and 
 Rf is a group having a linear or branched monooxyfluoroalkylene group or 
 polyoxyfluoroalkylene group having 4-20 carbon atoms. 
 
     
     
       10. The method according to  claim 9 , wherein Rf is a group of the formula:
   -A 1 O-(A 2 O) n -A 3 - 
 wherein A 1 O is an oxyfluoroalkylene group having 1-10 carbon atoms, 
 A 2 O is an oxyfluoroalkylene group having 2-5 carbon atoms, 
 A 3  is a fluoroalkylene group having 1-4 carbon atoms, and 
 n is an integer of 0 to 5, preferably an integer of 1 to 4. 
 
     
     
       11. The method according to  claim 9 , wherein the fluorocarboxylic acid is represented by the following general formula (II):
   X—(CF 2 ) m  —O—(CF(CF 3 )CF 2 O) n —CF(—Y)(CF   2 ) p , COOH   (II)
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, 
 Y is a hydrogen atom, a fluorine atom or CF 3 , 
 m is an integer of 1 to 10, 
 n is an integer of 0 to 5, and 
 p is 0 or 1. 
 
     
     
       12. The method according to  claim 9 , wherein the fluorocarboxylic acid is represented by the following formula (IIa) or (IIb):
   X—(CF 2 ) m —O—(CF(CF 3 )CF 2 O) n —CF(CF 3 )COOH   (IIa)
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, 
 m is an integer of 1 to 10, and 
 n is an integer of 0 to 5, or
   X—(CF 2 ) m —O—(CF(CF 3 )CF 2 O) n —CHFCF 2 COOH   (IIb)
 
 
 wherein X is a hydrogen atom, a fluorine atom or a chlorine atom, 
 m is an integer of 1 to 10, and 
 n is an integer of 0 to 5. 
 
     
     
       13. The method according to  claim 9 , wherein the fluorocarboxylic acid having an ether is CF 3 —O—CF(CF 3 )CF 2 O—CF(CF 3 )COOH. 
     
     
       14. The method according to  claim 9 , wherein the fluorocarboxylic acid is 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy]-propanoic acid or salts thereof. 
     
     
       15. The method according to  claim 1 , wherein the activation treatment is a steam activation treatment. 
     
     
       16. The method according to  claim 1 , which further comprises adjusting a pH level of the liquid containing the fluorocarboxyclic acid by adding an acid.